INSTRUMENTS WITH A DIGITAL SOUL
Contactless temperature measurement and diagnostics
Huge development of thermometry and thermography resulted in a large number of contactless thermometers and thermovision systems available on the market. Infrared thermometers are also called pyrometers. Their main advantage is non-intrusive measurement.
Features of infrared measurements
- No heat exchange between the measured object and the temperature sensor,
- No temporary change in temperature distribution in the point of contact of the sensor and the object,
- No need to wait for temperature stabilization, i.e. levelling the sensor temperature and the temperature of the object under measurement.
Using pyrometers in thermal diagnostics
Measurement with the use of infrared thermometers as well as monitoring and recording the results significantly enhances the possibilities in the field of temperature diagnostics and dynamic measurements. Temperature (thermal) diagnostics includes spatial and time-related temperature changes. With the use of continuous monitoring or periodical controls, you can evaluate the technical condition of numerous devices and components, conduct temperature supervision of various processes, like production, operational (physical and chemical), or logistics and storage processes.
Selected application areas for contactless temperature measurement
- Operational supervision of bearings and rollers,
- Diagnostics of electronic ICs and PCB components,
- Temperature control of electrically-live components and devices,
- Temperature measurements in EX zones,
- Temperature measurements of small volume components,
- Temperature control in storage and production facilities.
The influence of temperature on machine bearings
When operating machines with rotating elements or other moving parts, excessive heating results from increased friction, mismatching of moving parts, or changes in force distribution. The most vulnerable parts are bearings of any type. In this case, increased temperature clearly indicates:
- wear and tear,
- changes in geometry, forces, or the centre of gravity of the rotating system (imbalance),
- insufficient or excessive amount of grease,
- inappropriate technical parameters of the grease. Periodical temperature control of bearings and their seats with the use of a pyrometer is important, as it allows you to evaluate the technical condition of the system and make predictions.
Temperature of guide rollers
The effects of increased temperature are also visible in moving components, where guide rollers are used. Temperature control of roller systems allows you to easily diagnose them and locate particular rollers with noticeably different kinetic properties.
Diagnostics of electronic components and PCB boards
Another significant application area for temperature diagnostics contains electronic components and PCB boards. Due to the compact dimensions of the SMD and THT components, a contactless thermometer with high optical resolution is a perfect, and quite often the only way of conducting temperature diagnostics on a PCB board. This is caused by space limitations as well as potential threat of creating a short circuit with a temperature probe.
Chip control
When conducting temperature measurement of integrated circuits, semiconductors, capacitors, heatsinks, and housings, you can evaluate the technical conditions and diagnose any abnormal operations within the system resulting from inappropriate temperature of particular components. Controlling and measuring the temperature of semiconductors and cooling systems with heatsinks is relatively easy. Some semiconductor systems operate in high temperature ranges. They are close to the maximum temperature due to high values of conducted currents or high losses caused by connection resistance. Using local (spot) temperature measurement, it is possible to locate defective connections with increased resistance and local short circuits in insulation components. Furthermore, with the use of a pyrometer, you can easily determine temperature distribution over the surfaces of heatsinks and housings that quite often act as heat dissipation systems in integrated electronic modules.
Evaluating the temperature of transformers, coils and resistors
Contactless thermometer is irreplaceable in estimating the temperature of transformers, coils, resistors, and other electronic components of irregular shapes, with no flat surfaces and coated with insulating varnishes with high heat resistance, where the measurement can be conducted with the use of traditional electronic thermometers. What is more, when measuring the temperature of conductive live components, it is often impossible to use traditional thermometers with resistive probes or thermocouples.
Pyrometer as a natural way of creating insulation
Temperature measurement with the use of a pyrometer ensures natural and optimum galvanic insulation from a live object under measurement. During such measurement, the thermometer may be damaged, and the operator may incur an electric shock, as the thermometer is galvanically connected to an electrical circuit. Contactless temperature measurement eliminates these risks and allows for safe temperature diagnosis of electrical parts and components in operational conditions, even at very high voltages.
Measurements of chemical substances and process systems
Applying contactless temperature measurement increases the safety and reduces the risk in case of measurements of hazardous chemical substances or containers and process systems for storing or processing such substances. Thanks to a pyrometer, it is possible to easily allocate danger zones, reduce the PPE, and eliminate expensive dedicated thermometer and sensor solutions. An example of this can be found in the petrochemical industry or in manufacturing and packaging of flammable chemical substances.
Measurements of small volume components
Another application area for pyrometers is in measurements of small volume components and parts, where the dimensions and thermal capacity of the measured object are comparable with the dimensions and capacity of the temperature sensor. In such a case, when the two come into contact, an intensive heat exchange occurs as a result of the differences in temperatures of the sensor and the object, and consequently the temperature of the object noticeably changes. This means that during the measurement, the touch sensor (PT100, thermocouple, NTC, or semiconductor) very intensively cools down or heats up the object, or the temperature distribution locally changes. Such a long-lasting process of temperature determination of the object significantly impacts the reliability and accuracy of the measurement.
Measurement time in rated conditions
Providing that you know the time constant of your time sensor, you can determine the time required for conducting a measurement in rated conditions. In practice, it is 3 or 5 times the time constant. Time constant τ of a thermometer is the time required to achieve 63% of the total change amplitude. In case of measurements with the use of a pyrometer, determining temperature is not an issue, and it can be a lot quicker, without the necessity of considering the time constants. The only delay is connected with the measurement time of the device, which is a lot shorter and usually takes no longer that several milliseconds.
Infrared in warehouse areas
A huge application area for infrared thermometers is the warehouse and production space with imposed temperature (climate) standards. Detailed temperature recommendations apply at the stage of production, storing, and transport of food and pharmaceuticals. These recommendations regarding continuous, periodical, or occasional temperature control result from:
- applicable standards (international, national, industry, and corporate),
- widely accepted “best practices”, e.g. GMP or GDP,
- industry standards, such as the HACCP system for food or the FARMAKOPEA system for pharmaceutics.
Pyrometers in food and pharmaceutics industry
In general, contactless pyrometers are not designed for temperature monitoring and recording in food and pharmaceutics industries. However, due to the rapid and contactless measurement, they can be used in the following situations:
- where local temperature changes may occur, and where no traditional thermometers are used, e.g. large volume storage and logistics areas, production halls, etc.
- when the results are inconclusive and measurement comparison between various thermometers is required,
- during periodical or occasional inspections,
- during a failure of a cooling system or temperature monitoring system.
The influence of the emission factor on the measurements
When using infrared thermometers, you need to remember that the accuracy of the measurement results rely on the knowledge of the emission factor of an object under measurement. The actual temperature inside the object and the average temperature of the entire object may differ from the temperature of the surface layer and directly on the surface where the contactless measurement is conducted.
Pyrometer calibration
An infrared pyrometer can be checked and calibrated by comparing its results with a reference thermometer (usually, a traditional thermometer with PT100, RTD, or thermocouple), and then by selecting the appropriate value of the emission factor. Another way for improving the accuracy is by setting directly the emission factor, if it is known or precisely determined. Most of the pyrometers available on the market provide measurements within the emission factor range of 0.1 to 1. Additionally, the devices are equipped with the functionality of stepless adjustment of the factor value.
Defining the value of the emission factor
Remember that typical values for emission factors of common materials are tabulated and widely available. However, the emission factor depends not only on the material itself. Very often, the physicochemical composition of the surface of a diagnosed component influences the effective value of this parameter. For instance, a copper surface will have the emission factor below 0.1, an oxidised copper surface will have the emission factor of 0.6÷0.7, and for patinated oxidised copper surface the factor may increase to 0.9.
Differences in the values of the emission factor
Huge dispersion of the emission factor values applies to almost all metal surfaces that undergo the processes of oxidisation and corrosion, or that are under physical influence. In case of plastics and natural materials of similar composition, the changes of the emission factor may reach up to twenty percent.
Active measurement surface
Another important element that has to be considered during temperature measurement with the use of a contactless thermometer is defining the active measurement surface, in accordance with the optical resolution of the device. Optical resolution is the ratio of D (the distance between the thermometer and the object) to S (the diameter of the measurement area). If the optical resolution equals 10:1, the diameter of the circle being the measurement area is 10mm for the measurement distance of 100mm.
Optical resolution
High optical resolution noticeably improves the measurement capabilities of a thermometer, as the measurement is more selective and it is conducted on a proportionally smaller surface. This eliminates averaging temperature measurement results from a larger surface. For spot measurements, in case of very small surfaces, high-resolution (up to 100:1) contactless thermometers are used.
Summary
It should be noted that high speed and ease of measurement is crucial with infrared thermometers, as is the contactless character of the measurement. These features make pyrometers very useful devices.